Generally, cold production addresses a constantly changing need and, these days, represents a significant proportion of world electricity consumption used notably for conditioned air and the conservation of foodstuffs, and this despite the fact that the efficiency of the conventional refrigeration techniques based on gas compression and expansion remain inadequate.
The first refrigerants such as ammonia, sulfer dioxide, carbon dioxide or methyl chloride were very poisonous to people and the environment. They were replaced by chlorofluorocarbons, which were themselves prohibited in the early years of the new millenium because of their contribution to the greenhouse effect and the damage to the ozone layer. This problem remains since the hydrochlorofluorocarbons that are currently used continue, in lesser proportions, to have the same damaging effects as the earlier refrigerants.
In this context, there is therefore a two-fold advantage, energy-wise and environment-wise, in developing new cold production techniques that make it possible, on the one hand, to eliminate the refrigerant gases and, on the other hand, improve energy efficiency. Alternative techniques that can notably be cited include: thermoacoustic refrigeration, thermoelectric refrigeration or even magnetic refrigeration.
The latter relies on the magnetocaloric effect (EMC) of certain materials, which consists of a variation of their temperature when they are subjected to a magnetic field. It is thus sufficient to subject these materials to a succession of magnetization and demagnetization cycles and to perform a heat exchange with a heat-transfer fluid to obtain the widest possible temperature variation. The efficiency of such a magnetic refrigeration cycle exceeds that of a conventional refrigeration cycle by approximately 30%.
This energy saving that can be achieved with magnetic refrigeration makes it particularly interesting for domestic or industrial air conditioning or refrigeration applications.
The magnetocaloric effect (EMC) is at its maximum when the temperature of the material is close to its Curie temperature, the Curie temperature (Tc) being the temperature at which the material loses its spontaneous magnetization. Above this temperature, the material is in a disordered state called paramagnetic state.
Some magnetic materials such as gadolinium, arsenic or certain alloys of MnFe type exhibit magnetocaloric properties that are particularly well suited to the abovementioned applications.
Among these alloys, and notably based on Si, it is known practice, depending on the Curie temperatures sought, to be able to use alloys based on LaFeSiCo or based on LaFeSi(H). The insertion of light atoms such as hydrogen or cobalt into the LaFeSi compounds can be an effective way of increasing the Curie temperature while keeping the EMC effect of the material high. Such materials are particularly interesting because of their magnetocaloric properties combined with production costs, allowing for mass market applications, that are more favorable than those of materials such as gadolinium.
Generally, to exploit the properties of such magnetocaloric materials, the magnetic cold technology relies on the interaction of these materials with a heat transfer liquid that can be water-based.
The material heats up almost instantaneously when it is placed in a magnetic field and cools down by a similar thermal dynamic when it is removed from the magnetic field.
During these magnetic phases, the material is passed through by the liquid, called heat-transfer liquid, which will either be heated up on contact with the material during a so-called magnetization phase, or be cooled down on contact with the material during a so-called demagnetization phase.
Conventionally, the heat transfer fluid circulates in rectilinear channels or emergent pores that exist in the magnetocaloric material, this circulation corresponding to laminar mode hydraulic flow of the fluid, so as to obtain a maximum exchange surface area, with a minimum hydraulic head loss.
Thus, a cycle comprises:                a magnetization phase (magnetic stat=1);        a demagnetization phase (magnetic state=0) which is reflected in energy available in each phase.        
This cycle is repeated up to frequencies of several hertz. When the frequency increases, the thermal power (for example: the cooling) delivered by the apparatus also increases.
For this power to increase in proportion to the increase in frequency, it is necessary to have heat exchange characteristics between the material and the liquid which make it possible to increase this thermal flow.
The geometry of a part made of magnetocaloric material is therefore essential to ensure an optimum heat exchange between said part and the heat transfer fluid which circulates in contact therewith.
It is known practice to use lamellar structures of magnetocaloric material that allow the circulation of fluid between said blades and thus increase the exchange surface areas with the heat transfer fluid.
It is then necessary to reproducibly, constantly and very accurately gauge the distances between said blades of material so as to best control the heat exchange processes. This necessitates the use of mutual blade positioning elements while ensuring the control of the geometrical parameters necessary for obtaining satisfactory heat exchange characteristics.
In this context, the present invention proposes an optimized part structure made of magnetocaloric material and a method that makes it possible to produce such a part, whereas the conventional techniques currently deployed do not make it possible to achieve the form ratios necessary for optimizing the heat exchanges, because of excessively small dimensions to be achieved in mass parts.
More specifically, the subject of the invention is a one-piece part, namely made of a single piece, based on at least one magnetocaloric material made of an alloy comprising iron and silicon and at least one lanthanide, characterized in that:                said part comprises a base situated in a first plane defined by a first direction Dx and by a second direction Dy at right angles to the first direction Dx and a set of N unitary blades La,i secured to said base;        said blades having a first dimension DLai,x in the first direction, a second dimension DLai,y in the second direction and a third dimension DLai,z in a third direction Dz at right angles to the first and second dimensions;        an ith blade being substantially parallel to and separated from an (i+1)th blade by an ith distance di;        the ratio between the second dimension DLai,y and the first dimension DLai,x being greater than or equal to 10;        the ratio between the third dimension DLai,z and the first dimension DLai,x being greater than or equal to 6;        the first dimension DLai,x being of the same order of magnitude as said distance di separating an ith blade from an (i+1)th blade.        
Particularly suitable dimensions can lie within the following ranges:
0.1 mm≤DLai,x≤0.8 mm;
10 mm≤DLai,y≤100 mm;
5 mm≤DLai,z≤25 mm and being able preferably to be of the order of 12 mm.
According to a variant of the invention, the distance between an ith blade and an (i+1)th blade lies between approximately 0.1 mm and 1 mm.
Advantageously, another subject of the present invention is a complex part comprising two one-piece parts according to the invention, said two parts being embedded head-to-tail, making it possible to reduce the free space between blades.
According to a variant of the invention, the blades comprise convex upper surfaces.
According to a variant of the invention, said base comprises hollowed-out surfaces between an ith blade and an (i+1)th blade.
Advantageously, the profile of the hollows can be of concave type, the hollows having a radius of curvature optimized in such a way as to reinforce the velocity of a heat transfer fluid intended to circulate between the blades. Typically the radius of curvature can be of the order of 0.1 mm.
Typically, the number of blades of the one-piece part can be between ten or so and thirty or so blades.
It should be noted that it may be advantageous to manufacture thermal generation devices comprising magnetocaloric elements operating at different Curie temperatures and therefore parts made of different magnetocaloric materials, these parts having to be easily recognizable through the presence of marking elements.
This is why, according to a variant of the invention, the set of blades comprises at least one blade of third dimension different from that of the other blades making it possible to constitute a marking of said one-piece part. The positioning of the blade La,i concerned in the set of the blades La,1, . . . , La,N being relative to a given Curie temperature.
Similarly, a distinctive sign can also be incorporated on the base, more particularly in this case, said base comprises at least one surface between an ith blade and an (i+1)th blade, hollowed out differently from the other hollowed out surfaces, making it possible to constitute a marking of said one-piece part.
Advantageously, in a configuration with two blocks fitted head-to-tail, a blade of third dimension greater than that of the other blades of the block will be fitted in a base hollowing of conformal dimensions, which will allow for a relative positioning of the two blocks guaranteeing fluid blade thicknesses that are even and that conform to the specifications. These noteworthy dimensions can therefore fulfill a marking and positioning function or just one of these functions.
So as to optimize the fluid flow configurations through the one-piece part, the ratio between the dimension in the third direction of the base DE,z and the dimension in the second direction of the base DE,y lies between approximately ⅕ and 1/30;                the ratio between the dimension in the third direction of the base DE,z and the third dimension DLai,z is of the order of 1/20;        the first dimension DLai,x being preferentially substantially equal to the dimension in the third direction of the base DE,z.        
According to a variant of the invention, the base being made of a base material, the blades are made of at least one magnetocaloric material, the base material and the magnetocaloric material being different. Typically, the base can be produced in a non-magnetocaloric material that is less expensive than a magnetocaloric material.
According to a variant of the invention, the one-piece part comprises at least two series of blades made of at least two different magnetocaloric materials. Thus, by mixing, for example, different magnetocaloric materials and therefore Curie temperatures, it is possible to finely tune a part and its thermal characteristics to a specific set of specifications.
According to a variant of the invention, the magnetocaloric material is a composite material comprising at least one powder of a first magnetocaloric material and an organic binder.
In order to produce, in all these possible variants, a one-piece part according to the present invention, the Applicant considered that an extrusion or co-extrusion method was particularly well suited to all of the constraints imposed in terms of dimensioning to obtain excellent thermal performance levels, and do so in correlation with mass industrial development constraints.
This is why another subject of the present invention is a method for manufacturing a one-piece part according to the invention, characterized in that it comprises the following steps:                the continuous introduction, into at least one extruder body (Ex) comprising at least one heating sheath (Fi), of at least one powder of magnetocaloric material or a mixture of at least one magnetocaloric material with an organic binder;        the mixing, the homogenization and the melting of said powder of magnetocaloric material and, if appropriate, of the binder, by at least one extrusion screw (Vi) situated in the extruder body or bodies;        the shaping of said mixture comprising said magnetocaloric material through at least one extrusion die (fil), equipped with at least one imprint, making it possible to shape a one-piece part according to the invention;        said at least one die defining the structure of said one-piece part.        
According to a variant of the invention, the method further comprises a step of gradual cooling in the space, at the output of said at least one die, using dedicated means.
According to a variant of the invention, the dedicated means comprise a shaping tool comprising at least one section equipped with at least one channel in which a cooling/tempering fluid can circulate.
According to a variant of the invention, the die comprises a plurality of sections each comprising an imprint, at least two sections being separated by a thermal insulation plate whose thickness is determined to allow a temperature difference between the two sections.
According to a variant of the invention, the extruding body or bodies each comprise two co-rotating screws.
According to a variant of the invention, the method comprises:                the continuous production of a set consisting of strips of magnetocaloric material, secured to a base;        an operation of cutting said set so as to define individual one-piece parts.        
According to a variant, the method comprises the introduction of different materials through different feed means distributed along the extruder body or bodies.
According to several variants, the method may comprise the introduction through a feed means of an organic binder so as to produce a composite material comprising at least one powder of magnetocaloric material or comprise the introduction of a magnetocaloric material previously mixed with a binder. A second binder can, in this second variant, be introduced into the extruder.
According to a variant of the invention, said one-piece part being made up spatially of different materials in the second direction Dy, the method comprises the sequenced introduction of the different magnetocaloric materials so as to produce a set of continuous strips exhibiting sequences of different magnetocaloric materials, secured to a base, and the cutting of unitary one-piece parts from said set of strips.